Adolescent-onset cannabis users showed significantly slower verbal learning linked to disrupted activation patterns in the parahippocampal gyrus, midbrain, and thalamus.
Adolescents and young adults who use cannabis, parents, educators, neuroscience researchers
Cannabis users showed significantly slower verbal learning (p = 0.032)
What the researchers found
Cannabis users showed significantly slower learning across repeated trials (p = 0.032). Non-users progressively increased activation in the midbrain, parahippocampal gyrus, and thalamus during learning, while cannabis users showed greater but disrupted activation in these same regions.
Why it matters
The disrupted activation patterns suggest cannabis users recruit the same brain regions for learning but do so in a disorganized way, which may explain the cognitive difficulties commonly reported by regular users.
The numbers in context
21 cannabis users vs 21 non-users; learning significantly slower (p = 0.032, partial eta-squared = 0.108); at least 12 hours abstinent; progressive midbrain/parahippocampal/thalamus activation disrupted in users
How the study worked
Functional MRI study comparing 21 adolescent-onset regular cannabis users and 21 non-users during a paired associate verbal learning task, performed at least 12 hours after last cannabis use.
What this study cannot tell us
Small sample, cross-sectional design cannot establish causation, 12-hour abstinence may not eliminate all acute effects, no pre-use baseline data available.
How to read the evidence
Small fMRI study with matched controls but cross-sectional design
When this study was published
Published in 2021. Neuroimaging research on cannabis and cognition continues to refine understanding of specific affected brain circuits.
The bigger picture
These findings provide a neurological explanation for the learning difficulties associated with adolescent cannabis use, showing that the brain regions essential for learning new information are functionally disrupted.
Questions still open
- Do these disrupted activation patterns normalize after extended abstinence? Is there a threshold of cannabis use below which these effects do not occur? Would cognitive training help cannabis users overcome these learning deficits?
Common questions
Does cannabis affect learning ability?
Which brain regions are affected?
Read the original research
Disrupted parahippocampal and midbrain function underlie slower verbal learning in adolescent-onset regular cannabis use.
Psychopharmacology, 238(5), 1315-1331
Citation
Blest-Hopley, Grace; O'Neill, Aisling; Wilson, Robin; Giampietro, Vincent; Bhattacharyya, Sagnik. (2021). Disrupted parahippocampal and midbrain function underlie slower verbal learning in adolescent-onset regular cannabis use.. Psychopharmacology, 238(5), 1315-1331. https://doi.org/10.1007/s00213-019-05407-9
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